The present invention relates to a closing device having a safety for the following purpose: When a closing element that moves across an opening closes the opening, the safety function keeps objects that may be located in the opening from being trapped and damaged.
An important area of applications for closing devices of this kind is, for example, the side windows or roof windows of motor vehicles in the case of which a window pane or, respectively, sunroof is moved with the help of an electric drive motor.
Per the legal regulations, closing devices of this kind for vehicle windows are to have a trapping protection function that is designed to, to as great an extent as possible, keep users from being injured if they trap body parts. This protection function is achieved by limiting the closing force exerted by the closing device to 100 N.
As a general rule, this is achieved via, for example, closing devices in which the speed of the closing element, the torque exerted by its drive motor, or a force acting on the closing element in the opposite direction to its movement is detected, the closing movement being reversed if changes in these detected values indicate that an object may be trapped in the opening.
It has become clear that simply limiting the closing force to a maximum of 100 N does not provide adequate protection against injuries to the user if, for example, his or her hand or individual fingers accidentally become trapped. Therefore efforts have been made to develop closing devices having trap protection that exert a lower maximum force. However, problems arise if the closing devices are exposed to vibration during operation, in particular if they are used as closing devices for the window panes or sunroof of a motor vehicle. These vibrations cause parameters such as motor torque and counterforce, which are monitored by the closing device in order to limit the closing force, to fluctuate temporarily. The lower the predefined maximum closing force of the closing device, the easier it is for the parameter that is being monitored to exceed a limit value for which the closing device detects that the maximum closing force has been exceeded and thereupon interrupts or reverses the closing movement. For example, with a device of this kind it may be impossible to close the side window of the motor vehicle when the vehicle is driving across uneven terrain.
In order to tackle this problem, German Published Patent Application No. 4020351 proposes a closing device to which a sensor element supplies measured signals resulting from acceleration forces exerted on the vehicle body in the vertical direction. The accelerations measured this sensor element are offset against the monitored parameters of the closing device, which are measured simultaneously so that the disruptive influence of these accelerations can be suppressed.
It is true that this technology ensures that the closing device functions more reliably even if the closing force limit values are lower than the 100 N permitted by law; however, for various reasons it is not totally satisfactory.
One problem is that as a general rule the mechanical structure of the closing device is not absolutely rigid, so that as a result of external vibrations the closing element or its drive mechanism may start to vibrate, and as a result force peaks greater than the closing force limit values may be detected at the drive motor even after the external vibration has already decayed. The known device cannot compensate for reverberation of this kind, so that undesired reversing may still occur as a result of vibration during the closing movement.
Another problem is that frictional resistance arising when the closing element moves up and down its guideway or arising in the drive mechanism of the guideway element can also cause the parameter that is monitored to exceed the limit value at which the closing device detects that the closing force limit value has been exceeded. If, for example, the parameter that is being monitored is the torque exerted by the drive motor of a window raiser, it is clear that this will increase not only if an object has been trapped between the window pane and its frame but also if there is frictional resistance that keeps the window pane from moving freely up and down its guideway. Such frictional resistances may increase during the operating life of a closing device due to wear and tear; in addition, for design-related reasons they may have different values at different points in the closing movement. In the case of the known closing device, the only way to take this into account is to ensure that the chosen closing force limit value is not too low and in particular to ensure that when one defines the limit value a safety margin is calculated in to reflect the possibility that with increasing age the closing device will start to encounter greater frictional resistance.
In the case of the present invention, a closing device, in particular for the window or sunroof of a motor vehicle which allows one to choose a sufficiently low closing force limit value is provided, the closing movement being interrupted, or reversed if the limit value is exceeded, so that there is no absolutely no risk of injury if a body part becomes trapped in the opening to be closed. Because the closing force limit value can be varied, this limit value can be calculated very precisely for normal operating conditions, without the need for a safety margin for taking into account uneven distribution of frictional forces across the range of closing movement or due to aging of the closing device. Because the device varies the limit value based on force exerted on the closing element that has been measured at an earlier point in time, it can filter out vibrations to which the closing element is exposed, a separate sensor for this purpose being unnecessary. By choosing a suitable time period during which a variation in the limit value lasts, the device can be rendered insensitive to reverberation phenomena in the closing element following external vibration or, respectively, in the drive mechanism used to transfer the closing force of a motor to the closing element, which can cause the force to be exerted by the motor to fluctuate.
Preferably the force limit value is varied in such a way that if the sensor which detects the force exerted on the closing element in the direction opposite to closing detects an abrupt decrease in this force, the control circuit increases the lit value for a limited time period or for a limited stretch of the closing element""s path. This is based on the realization that an abrupt decrease in the force is generally due to the fact that the object on which the closing device is mounted is being accelerated downwards and that an upward acceleration will follow immediately once the object""s downward movement comes to an end. In the case of a motor vehicle, this situation occurs, for example, when the vehicle drives off a curbstone or into a recess such as a pothole. The upward acceleration causes the force in the direction opposite to the closing movement to increase but is not due to trapping of an object and is therefore ignored by the closing device according to the present invention by the limit value being increased at the point in time when this force arises.
Herein, in particular, the control circuit may detect the length of a time period or length of stretch of the closing element""s path during which the decrease in the force lasts. It is reasonable to anticipate that the acceleration in the opposite direction will be roughly of the same absolute value and will last for roughly the same time; therefore it is useful if the time period or the length of stretch of the path during which limit value is increased is chosen to be exactly equal to, or better still, given that there may be vibration phenomena, greater than the length that has been detected.
It is useful if the amount by which the limit value is increased as a result of a downward acceleration is proportional to the downward acceleration measured during the period during which the decrease in force lasted.
According to a preferred further refinement of the present invention, the control circuit determines the change in force based on the distance traveled by the closing element and increases the limit value if the force as a function of distance traveled increases at a rate higher than that defined by a limit spring rate.
If the increase in force is due to the vehicle having been accelerated upwards, it generally occurs within small fractions of a second, which correspond to a distance traveled by the closing element of just a few millimeters or fractions of a millimeter, i.e., corresponding to a high spring rate. In this case, undesired reversing of the losing device can be suppressed by increasing the limit value. If a body part is trapped, the increase in force is, by comparison, significantly less rapid. Injury associated with trapping of body parts can be prevented by using a low force limit value in conjunction with a low spring rate. A suitable value for the limit spring rate is, for example 20 N/mm or more. A simple way to increase the force limit value is for the control circuit to temporarily interrupt monitoring of the force.
According to a particularly preferred feature of the present invention, the closing device includes a memory for storing force values for a given position or plurality of adjacent positions of the closing element. The stored force values may be force values measured at the positions in question or limit values that are valid for the positions in question. These values may be predefined so that each one is different for a given position of the closing element so as to reflect the fact that the closing force to be exerted may vary due to the design of the closing device.
It is useful if these force values or limit values are updated on an ongoing basis by generating sliding averages of the forces exerted on the closing element at given positions so that wear-and-tear phenomena, dirt etc. to which the closing device is subject may be taken into account.
It is useful that force values measured during a closing movement are not used to update the sliding averages until it has been determined that a deviation in a measured force value relative to the corresponding stored value has not resulted in interruption of the closing movement. This means one can avoid a situation where the sliding averages are calculated incorrectly using measured force values associated with an actual trapping event.
Furthermore, it is preferred if each stored force value is obtained by generating the mean for a plurality of adjacent positions of the closing element. This saves memory space; moreover, by generating the mean by carrying out averaging for a plurality of positions in the course of a closing movement one can largely suppress the impact of individual erroneous measurements.
Further features and advantages of the present invention are set forth in the description below and with reference to the figures.